Adhesive agent

ABSTRACT

Provided are a pressure-sensitive adhesive having excellent durability and reliability under high-temperature or high-humidity conditions, adhesion strength, workability, re-movability, and the ability to inhibit light leakage; a method for preparing the pressure-sensitive adhesive; a polarizer including the pressure-sensitive adhesive; and a liquid crystal display incorporating the polarizer.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional of U.S. patent application Ser. No.13/059,923, filed Feb. 18, 2011 which is the U.S. National Phaseapplication of International Application No. PCT/KR2009/004652, filedAug. 20, 2009, and claims the benefit of Korean Application No.10-2008-0081317, filed on Aug. 20, 2008, all of which are herebyincorporated by reference in its entirety for all purposes as if fullyset forth herein.

BACKGROUND

1. Field of the Invention

The present invention relates to a pressure-sensitive adhesive, a methodfor preparing the pressure-sensitive adhesive, a polarizer, and a liquidcrystal display.

2. Discussion of Related Art

A polarizer is an optical member included in a liquid crystal display(LCD). A polarizer has a multilayer structure that includes iodinecompounds or dichromatic polarizing materials arranged in apredetermined direction; and protecting films (e.g. triacetyl cellulose(TAC)) for protecting a polarizing film or element. Further, thepolarizer may include additional films, such as a phase differenceplate, a wide viewing angle compensating plate, a brightness improvingfilm and the like, to improve its performance.

Each film constituting a multilayer polarizer is made of materialshaving different molecular structures and compositions, and thus showsdifferent physical properties. Particularly, these films lackdimensional stability under high temperature and/or high humidityconditions due to a difference in the shrinkage or expansion behaviorthereof. As such, when a polarizer is fixed by a pressure-sensitiveadhesive, the TAC layer, and any other layer, is subject to stressconcentration at high temperature and/or high humidity. As a result,birefringence is induced, and light leakage takes place.

To solve these problems, techniques for providing the adhesive with astress relaxation characteristic have been disclosed. Particularly, amethod of designing the adhesive so as to cause high creep and easydeformation under external stress has been disclosed (e.g. Korean PatentApplication Publication No. 1998-079266, Japanese Patent ApplicationPublication No. 2002-047468, etc.).

However, this technique has a drawback in that cuttability orworkability of the adhesive is significantly reduced. When thecuttability or workability of the adhesive is reduced, failure such asleakage or depression of the adhesive occurs when the polarizer ismass-produced, and thus the yield is remarkably lowered.

On the other hand, there have been attempts to design an adhesive withhigh hardness to minimize the light leakage.

For example, Japanese Patent Application Publication No. 2007-197659discloses a technique in which an adhesive composition is prepared byadding a multi-functional acrylate, an isocyanate hardener, and a photoinitiator to an acrylic copolymer containing a carboxyl group, and thenan adhesive is prepared by UV curing the adhesive composition. JapanesePatent Application Publication No. 2007-212995 discloses a technique inwhich an adhesive composition is prepared by mixing a copolymercontaining a hydroxyl group and a copolymer containing a carboxyl groupat a predetermined ratio and adding a multi-functional acrylate, amulti-functional isocyanate hardener, and a photo initiator to themixture, and then an adhesive is prepared by UV curing the adhesivecomposition.

However, the storage modulus (G′) of the adhesives disclosed in theprior art documents, is excessively increased, and thus initial adhesionis greatly reduced. Thus, durability is reduced at high temperature orhumidity. Further, when the storage modulus of the adhesive iscontrolled to be low, the hardness of the adhesive becomes insufficient,and thus a large quantity of light leaks out.

SUMMARY OF THE INVENTION

The present invention provides a pressure-sensitive adhesive, a methodof producing the pressure-sensitive adhesive, a polarizer that includesthe pressure-sensitive adhesive, and a liquid crystal displayincorporating the polarizer.

An aspect of the present invention provides a pressure-sensitiveadhesive including a hard area and a soft area, whereby the soft areahas a lower storage modulus than the hard area. The hard area and thesoft area are patterned within a single plane.

Another aspect of the present invention provides a method of producing apressure-sensitive adhesive. The method includes a first step of coatinga coating solution (e.g. a pressure-sensitive adhesive composition) forforming the pressure-sensitive adhesive on a substrate, and a secondstep of curing the pressure-sensitive adhesive composition coated on thesubstrate in the first step so as to form a pattern of hard areas andsoft areas.

Still another aspect of the present invention provides a polarizerincluding a pressure-sensitive adhesive, in which the pressure-sensitiveadhesive is formed on one or both surfaces of a polarizing film or apolarizing element.

Yet another aspect of the present invention provides a liquid crystaldisplay including a liquid crystal panel, in which a polarizer isattached to one or both surfaces of the liquid crystal panel.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent to those of ordinary skill in the art bydescribing in detail exemplary embodiments thereof with reference to theattached drawings in which:

FIG. 1 is a schematic plan view illustrating a pressure-sensitiveadhesive according to an exemplary embodiment of the present invention.

FIGS. 2 and 3 are schematic views illustrating a process of producing apressure-sensitive adhesive according to exemplary embodiments of thepresent invention.

FIGS. 4 through 9 are schematic plan views illustrating apressure-sensitive adhesive according to exemplary embodiments of thepresent invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present invention relates to a pressure-sensitive adhesive includinga hard area and a soft area, whereby the soft area has a lower storagemodulus than the hard area, the hard area and soft area being patternedwithin a single plane.

Hereinafter, the pressure-sensitive adhesive of the present inventionwill be described in greater detail.

The pressure-sensitive adhesive of the present invention is designed toinclude hard and soft areas within a single plane in a patterned state.The term “single plane” as used herein refers to a continuous planeformed by a single pressure-sensitive adhesive. Thus, the term “apattern of hard and soft areas formed within a single plane” refers tothe case in which at least two areas, one area having a higher storagemodulus than the other area, are patterned in a singlepressure-sensitive adhesive plane. For this reason, the case in whichthe pattern of hard and soft areas is formed by combining at least twopressure-sensitive adhesives having a uniform storage modulus isexcluded from the definition “pattern of hard and soft areas formedwithin a single plane” of the present invention. As mentioned above,when the pattern is formed using at least two pressure-sensitiveadhesives, the productivity of optical members such as a polarizer isremarkably reduced, and an effect similar to a single plane cannot beproduced due to different physical properties between thepressure-sensitive adhesives forming the pattern. For example, when thepressure-sensitive adhesive is applied to an optical member such as apolarizer, the contacts (interfacial parts) of the at least twopressure-sensitive adhesives are susceptible to failure, and problemswith durability easily arise because the pressure-sensitive adhesiveshave different shrinkage rates and storage moduli. Further, when the atleast two pressure-sensitive adhesives are used, their contacts(interfacial parts) have high non-uniformity, and thus easily give riseto problems in the aspect of light transmission uniformity.

The term “hard area” as used herein refers to an area having a higherstorage modulus in the pressure-sensitive adhesive compared to anotherarea (e.g. a soft area). In the present invention, for example, the hardarea may have a storage modulus of 1 MPa to 50 MPa, preferably 1 MPa to40 MPa, and more preferably 1 MPa to 20 MPa at a temperature of 30° C.By setting the storage modulus of the hard area in this range, it ispossible to prevent adhesion or durability from being lowered while adimensional change caused by elongation of the polarizer is inhibited.

Further, the term “soft area” as used herein refers to an area having alower storage modulus in the pressure-sensitive adhesive compared toanother area (e.g. a hard area). For example, the soft area may have astorage modulus of 0.01 MPa to 5.0 MPa, preferably 0.01 MPa to 0.1 MPa,and more preferably 0.1 MPa to 1 MPa at a temperature of 30° C. In thepresent invention, by setting the storage modulus of the soft area inthis range, it is possible for the soft area to effectively support thehard area, and thus to effectively inhibit shrinkage and expansion ofthe polarizer while the workability of the pressure-sensitive adhesiveand the yield of the polarizer are excellently maintained. Further, asthe storage modulus of the soft area is set in this range, it ispossible to prevent durability and adhesion properties from beingreduced due to an excessive increase in the entire storage modulus ofthe pressure-sensitive adhesive.

Further, the term “pattern” as used herein refers to the case in whichthe hard and soft areas have a predetermined shape in the singlepressure-sensitive adhesive plane. Here, the shape includes a linearshape, a quadrilateral shape, a circular shape or an elliptical shape,as well as an irregular shape, i.e. an amorphous shape.

In one embodiment, the hard area may be patterned in a linear shape, andpreferably in a continuous linear shape. In detail, thepressure-sensitive adhesive 1 of the present invention may include thehard areas 1-1 and the soft areas 1-2 patterned in a continuous linearshape as illustrated in FIG. 1.

In the case in which the hard and soft areas of the pressure-sensitiveadhesive are patterned in a linear shape, the hard areas may becontinuous, as illustrated in FIG. 1. Here, the term “continuous” refersto the state where the hard areas patterned in a linear shape continuethroughout the pressure-sensitive adhesive without interruption. In thiscase, the hard areas may be continuously formed in a direction parallelor perpendicular to an elongation axis of a polarizer to which thepressure-sensitive adhesive is applied. When exposed to high-temperatureor high-humidity conditions, the polarizer contracts or expands alongthe elongation axis thereof, over an entire surface thereof. Thus, whenthe hard areas of the pressure-sensitive adhesive are configured to becontinuous, light leakage caused by the shrinkage or expansion of thepolarizer under the conditions can be effectively inhibited.

When the hard areas have a linear pattern as mentioned above, the widthand interval of the linear pattern are not particularly limited, and canbe controlled according to the desired purpose. In the presentinvention, for example, in consideration of productivity, etc., the hardareas having a linear pattern may be configured to have a width of 90 μmto 1,000 μm, and an interval of 50 μm to 1.0 cm. Further, in the presentinvention, the width and interval of the linear pattern of hard areasmay be controlled to be equal to each other or different from each otheras needed. However, the line width and interval of the linear pattern ofthe hard areas are not limited to this configuration.

In the present invention, the ratio (G′_(hard)/G′_(soft)) of the storagemodulus (G′_(hard)) of the hard area to that (G′_(soft)) of the softarea may range from 3 to 100, preferably from 3 to 50, and morepreferably from 3 to 30. In the present invention, when the ratio isless than 3, an effect obtained by patterning the pressure-sensitiveadhesive with different storage moduli may become insignificant. Whenthe ratio is more than 100, the difference between the storage moduli ofthe hard and soft areas is too excessively, and thus the physicalproperties of the pressure-sensitive adhesive become non-uniform,durability is reduced, or haze may occur due to a difference inrefractive index.

Further, in the present invention, the hard area may have an area ratioof 10% to 60%, and preferably 15% to 50%, relative to the entire area ofthe pressure-sensitive adhesive. Here, the term “entire area of thepressure-sensitive adhesive” refers to an entire area of a single planeformed by the single pressure-sensitive adhesive. In the presentinvention, when the hard area occupies less than 10% of the entire area,an overall hardness of the pressure-sensitive adhesive may be too low,workability, cuttability, and productivity may be degraded, or strainderived from the elongation axis of the polarizer may not be effectivelyinhibited, so light leakage may occur. Further, when the hard areaoccupies more than 60% of the entire area, the hardness of thepressure-sensitive adhesive may be too high, and thus the adhesion anddurability may be reduced.

In the present invention, the pressure-sensitive adhesive including thepattern of hard and soft areas as described above may have a gel contentexpressed by the following Equation 1 within a range of 50% to 99%,preferably 80% to 99%, and more preferably 90% to 99%.Gel Content=B/A×100  [Equation 1]where A represents the weight of the pressure-sensitive adhesive, and Brepresents the weight of the dried product of the undissolved parts ofthe pressure-sensitive adhesive, the weight of the dried product beingmeasure after depositing the pressure-sensitive adhesive in ethylacetate for 72 hours at room temperature, and drying the deposits.

The term “the weight of the dried product” as used herein refers to theweight of the undissolved components of the deposits, from which ethylacetate is removed by drying the deposits under suitable conditionsafter the deposition process. Here, the conditions for removing theethyl acetate are not particularly limited, as long as the ethyl acetateincluded in the deposits can be completely removed.

In the present invention, when the gel content is less than 50%, bubblesoccur under high-temperature or high-humidity conditions, and thus thedurability and reliability may be reduced. When the gel content is morethan 99%, peeling or lifting may occur under high-temperature orhigh-humidity conditions.

In the present invention, as described above, the componentsconstituting the pressure-sensitive adhesive in which the hard and softareas are included in a patterned state are not particularly limited. Inthe present invention, for example, the pressure-sensitive adhesive maybe prepared by curing a pressure-sensitive adhesive compositioncontaining an acryl resin, a multi-functional acrylate, and a photoinitiator.

In the present invention, the pressure-sensitive adhesive compositionmay be a photo-curable composition. Here, a photo-curable compositionrefers to a composition that can be cured by irradiating radiation.Meanwhile, the term “radiation” as used herein refers to energy rayscapable of causing a curing reaction by influencing a polymerizablegroup or a polymerization initiator included in the pressure-sensitiveadhesive composition, and includes electromagnetic rays and ultraviolet(UV) rays. Hereinafter, the term “UV rays” may be regarded as having thesame meaning as “radiation.”

In the present invention, the composition of the acryl resin asmentioned above is not particularly limited. For example, in the presentinvention, the acryl resin may include a polymer of a (meth)acrylic acidester monomer or a polymer of a monomer mixture comprising a(meth)acrylic acid ester monomer.

The kind of (meth)acrylic acid ester monomer that can be used in thepresent invention is not particularly limited. For example,alkyl(meth)acrylate may be used. In this case, when an alkyl groupincluded in the (meth)acrylic acid ester monomer is excessively long,the cohesion of the pressure-sensitive adhesive may be reduced, oradjustment of the glass transition temperature T_(g), or adhesionproperties may be difficult. As such, it is preferable to use analkyl(meth)acrylate having an alkyl group with 1 to 14 carbon atoms.Examples of this monomer may include methyl(meth)acrylate,ethyl(meth)acrylate, n-propyl(meth)acrylate, isopropyl(meth)acrylate,n-butyl(meth)acrylate, t-butyl(meth)acrylate, sec-butyl(meth)acrylate,pentyl(meth)acrylate, 2-ethylhexyl(meth)acrylate,2-ethylbutyl(meth)acrylate, n-octyl(meth)acrylate,isooctyl(meth)acrylate, isononyl(meth)acrylate, lauryl(meth)acrylate,and tetradecyl(meth)acrylate. In the present invention, one or a mixtureof at least two selected from these monomers may be used.

In the present invention, the acryl resin may be provided with acrosslinkable functional group as needed. In this case, the monomermixture constituting the polymer may include a (meth)acrylic acid estermonomer and a crosslinkable monomer. This crosslinkable monomer mayreact with a multi-functional crosslinking agent or a silane couplingagent, which will be described below, thereby functioning to improvephysical properties such as durability and cohesion underhigh-temperature or high-humidity conditions.

Examples of the crosslinkable monomer that can be used in the presentinvention include a monomer containing a hydroxy group, a monomercontaining a carboxyl group, and a monomer containing nitrogen At leastone of these monomers may be properly selected and used in considerationof the kind of the crosslinking agent included in the pressure-sensitiveadhesive composition. The present invention, above all, preferably uses,but is not limited to, a monomer containing a hydroxy group among thecrosslinkable monomers. Detailed examples of a monomer containing ahydroxy group include 2-hydroxyethyl(meth)acrylate,2-hydroxypropyl(meth)acrylate, 4-hydroxybutyl(meth)acrylate,6-hydroxyhexyl(meth)acrylate, 8-hydroxyoctyl(meth)acrylate,2-hydroxyethyleneglycol(meth)acrylate,2-hydroxypropyleneglycol(meth)acrylate, and so on. Examples of a monomercontaining a carboxyl group include (meth)acrylic acid,2-(meth)acryloyloxy acetate, 3-(meth)acryloyloxy propylate,4-(meth)acryloyloxy butyrate, acrylic acid dimer, itaconic acid, maleicacid, maleic acid anhydride, and so on. Examples of a monomer containingnitrogen include (meth)acrylamide, N-vinyl pyrrolidone, N-vinylcaprolactam, and so on. The crosslinkable monomer is not limited tothese monomers. In the present invention, one or a mixture of at leasttwo selected from these monomers may be used.

When the monomer mixture in the present invention includes thecrosslinkable monomer, the monomer mixture may, for example, include 80to 99.8 parts by weight of the (meth)acrylic acid ester monomer, and0.01 to 3 parts by weight of the crosslinkable monomer.

In the case where the monomer mixture includes the crosslinkablemonomer, the initial adhesion strength of the pressure-sensitiveadhesive may be reduced when the (meth)acrylic acid ester monomer isless than 80 parts by weight. When the (meth)acrylic acid ester monomeris more than 99.8 parts by weight, the cohesion may be reduced, so thereis a possibility there will be a problem with the durability.

Further, when the crosslinkable monomer of the monomer mixture is lessthan 0.01 parts by weight, the durability and reliability of thepressure-sensitive adhesive may be reduced. When the crosslinkablemonomer of the monomer mixture is more than 3 parts by weight, thereaction with the crosslinking agent and/or the silane coupling agentmay be excessively carried out, so that the tackiness and/or peelstrength may be reduced.

Further, in the present invention, a compound expressed by the followingFormula 1 may be additionally copolymerized in the acryl resin asneeded. The compound of Formula 1 may be added to adjust the glasstransition temperature and provide other functions.

where each of R₁, R₂ and R₃ independently represents hydrogen or alkyl,and R4 represents phenyl, acetyloxy or COR₅ substituted or unsubstitutedwith cyano or alkyl. Here, R₅ represents glycidylalkyloxy, glycidyloxyor amino substituted or unsubstituted with alkyl or alkoxyalkyl.

In the definitions of R₁ to R₅ of Formula 1, alkyl or alkoxy refers toalkyl or alkoxy having 1 to 8 carbon atoms, and preferably methyl,ethyl, methoxy, ethoxy, propoxy or butoxy.

Detailed examples of the monomer of Formula 1 include, but are notlimited to, one or at least two of a monomer containing nitrogen such as(meth)acrylonitrile, (meth)acrylamide, N-methyl(meth)acrylamide, orN-butoxy methyl(meth)acrylamide; a styrene monomer such as styrene ormethyl styrene; glycidyl(meth)acrylate; and a carboxylic acid vinylester such as vinyl acetate. In the case in which the monomer mixture ofthe present invention includes the compound of Formula 1, it ispreferable to have an amount of 20 parts by weight or less on the basisof the content of (meth)acrylate ester monomer. When the content of thecompound is more than 20 parts by weight, the softness and/or peelstrength of the pressure-sensitive adhesive may be reduced.

When the acryl resin is a polymer of a (meth)acrylate ester monomerand/or the functional monomer represented by Formula 1, the polymerpreferably has a weight-average molecular weight of 500,000 or more. Inthe acryl resin having the above-mentioned composition, when theweight-average molecular weight is less than 500,000, bubbles appear orpeeling occurs under high-temperature or high-humidity conditions due toa decrease in cohesion, and thus the durability and reliability may bereduced.

When the acryl resin in the present invention includes the crosslinkablemonomer as a monomer component, the acryl resin preferably has aweight-average molecular weight of 1,000,000 or more. When theweight-average molecular weight of the acryl resin is less than1,000,000, the durability and reliability of the pressure-sensitiveadhesive may be reduced.

In the present invention, the upper limit of the weight-averagemolecular weight of the acryl resin is not particularly limited. Forexample, the weight-average molecular weight of the acryl resin may beappropriately controlled within a range of 2,500,000 or less inconsideration of the durability and reliability or coatability of thepressure-sensitive adhesive, but it is not limited to this range.

In the present invention, a method of preparing the acryl resinincluding the components is not particularly limited. For example, theacryl resin may be prepared using an ordinary polymerization method suchas solution polymerization, photo polymerization, bulk polymerization,suspension polymerization, or emulsion polymerization. The acryl resinmay be preferably prepared by using solution polymerization. Thesolution polymerization may be carried out at a temperature of 50° C. to140° C. by adding an initiator when each monomer is mixed uniformly.Examples of the initiator that may be used in this process include anazo initiator, such as azobisisobutyronitrile or azohiscyclohexanecarbonitrile, and/or a typical initiator, such as a benzoil peroxide oracetyl peroxide. The initiator may use, but is not limited to, one or amixture of at least two selected from the initiators.

In the present invention, the pressure-sensitive adhesive compositionmay include a multi-functional acrylate in addition to the acryl resin.The multi-functional acrylate, for example, may serve to enhance thestorage modulus of the pressure-sensitive adhesive through reaction witha photo initiator, which will be described below.

The kind of multi-functional acrylate that may be used in the presentinvention is not particularly limited. In the present invention, themulti-functional acrylate may be, but is not limited to, a bifunctionalacrylate such as 1,4-butanediol di(meth)acrylate, 1,6-hexanedioldi(meth)acrylate, neopentylglycol di(meth)acrylate, polyethyleneglycoldi(meth)acrylate, neopentylglycol adipate di(meth)acrylate,hydroxypivalic acid neopentylglycol di(meth)acrylate, dicyclopentanyldi(meth)acrylate, caprolactone-modified dicyclopentenyldi(meth)acrylate, ethyleneoxide-modified di(meth)acrylate,di(meth)acryloxy ethyl isocyanurate, allylation cyclohexyldi(meth)acrylate, tricyclodecandimethanol(meth)acrylate, dimethyloldicyclopentane di(meth)acrylate, ethyleneoxide-modifiedhexahydrophthalate di(meth)acrylate, tricyclodecanedimethanol(meth)acrylate, neopentylglycol-modified trimethylpropanedi(meth)acrylate, adamantine di(meth)acrylate, or9,9-bis[4-(2-acryloyloxyethoxy)phenyl]fluorine; a trifunctional acrylatesuch as trimethylolpropane tri(meth)acrylate, dipentaerythritoltri(meth)acrylate, propionic acid-modified dipentaerythritoltri(meth)acrylate, pentaerythritol tri(meth)acrylate,propyleneoxide-modified trimethylolpropane tri(meth)acrylate,trifunctional urethane(meth)acrylate, ortris(meth)acryloxyethylisocyanurate; a tetrafunctional acrylate such asdiglycerin tetra(meth)acrylate or pentaerythritol tetra(meth)acrylate; apentafunctional acrylate such as propionic acid-modifieddipentaerythritol penta(meth)acrylate; and a hexafunctional acrylatesuch as dipentaerythritol hexa(meth)acrylate, caprolactone-modifieddipentaerythritol hexa(meth)acrylate, or urethane(meth)acrylate (e.g. areaction product of isocyanate monomer and trimethylolpropanetri(meth)acrylate) (e.g. UA-3061, UA-306T, etc. available from KyoeishaChemical Co. Ltd., Japan).

In the present invention, one or a mixture of at least two selected fromthese multi-function acrylates may be used. Particularly, an acrylatehaving a molecular weight of less than 1,000 and two functionalities,and preferably at least three functionalities, is used, so that superiordurability can be realized. The scope of the present invention is notlimited to this configuration.

Further, in one embodiment, a multi-functional acrylate having a ringstructure in its molecular structure may be used. When this kind ofacrylate is used, the pressure-sensitive adhesive may be formed in aharder state, and thus improve the inhibition of light leakage. In thiscase, the ring structure included in the acrylate may include any one ofan carbocyclic or heterocyclic structure, and a monocyclic or polycyclicstructure. Detailed examples of the multi-functional acrylate includingthe ring structure include, but are not limited to, a compound having anisocyanurate structure such as tris(meta)acryloxyethyl isocyanurate, andthe like; a hexafunctional acrylate such as an isocyanate-modifiedurethane(meth)acrylate (e.g. a reaction product of an isocyanatecompound and trimethylolpropane tri(meth)acrylate), or the like.

In the pressure-sensitive adhesive composition of the present invention,the multi-functional acrylate may be included in an amount of 5 to 40parts by weight relative to 100 parts by weight of acryl resin. When thecontent of the multi-functional acrylate is less than 5 parts by weight,the durability may be reduced under high-temperature conditions, and theability to inhibit light leakage may be reduced. When the content of themulti-functional acrylate is more than 40 parts by weight, durability athigh-temperatures may be reduced.

In the present invention, the composition constituting thepressure-sensitive adhesive may further include a photo initiator.

The kind of photo initiator that may be used in the present invention isnot particularly limited as long as it can induce a curing reaction ofthe pressure-sensitive adhesive composition by being irradiated with,for instance, UV rays. Examples of the photo initiator include benzoin,benzoin methylether, benzoin ethylether, benzoin isopropylether, benzoinn-butylether, benzoin isobutylether, acetophenone, dimethylaminoacetophenone, 2,2-dimethoxy-2-phenylacetophenone,2,2-diethoxy-2-phenylacetophenone,2-hydroxy-2-methyl-1-phenylpropane-1-on,1-hydroxycyclohexylphenylketone,2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propane-1-on,4-(2-hydroxyethoxy)phenyl-2-(hydroxy-2-propyl)ketone, benzophenone,p-phenylbenzophenone, 4,4′-diethylaminobenzophenone,dicyclobenzophenone, 2-methylanthraquinone, 2-ethylanthraquinone,2-t-butylanthraquinone, 2-aminoanthraquinone, 2-methylthioxanthone,2-ethylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone,2,4-diethylthioxanthone, benzyldimethylketal, acetophenonedimethylketal, p-dimethylamino benzoic acid ester,oligo[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone], and2,4,6-trimethylbenzoyl-diphenyl-phosphinoxide, and so on. In the presentinvention, the photo initiator may be, but is not limited to, one or amixture of at least two selected from the photo initiators.

In the pressure-sensitive adhesive composition of the present invention,the photo initiator may be included in an amount of 0.01 to 5 parts byweight relative to 100 parts by weight of acryl resin, or in an amountof 0.2 to 20 parts by weight relative to 100 parts by weight ofmultifunctional acrylate. By controlling the content of the photoinitiator within this range, the curable reaction of the composition maybe smoothly carried out, and it is possible to prevent the physicalproperties of the pressure-sensitive adhesive from being degraded due toresidual components after reaction.

In the present invention, the pressure-sensitive adhesive compositionmay further include a multi-functional crosslinking agent as needed.When this multi-functional crosslinking agent is additionally included,the pressure-sensitive adhesive may have an interpenetrating polymernetwork (IPN). The term “IPN structure” as used herein refers to thestate in which at least two crosslinking structures co-exist in a curingsystem of the pressure-sensitive adhesive. For example, when an acrylresin including a crosslinkable functional group is used in the presentinvention, and the multi-functional crosslinking agent is furtherincluded, a crosslinking structure (hereinafter, referred to as “firstcrosslinked structure”) formed by the reaction of the acryl resin andthe crosslinking agent, and another crosslinking structure (hereinafter,referred to as “second crosslinked structure”) formed by themulti-functional acrylate and the photo initiator may coexist in theadhesive, and thus the IPN structure may be realized. In this manner,the IPN structure is realized in the pressure-sensitive adhesive, andthe balance of the overall physical properties required for thepressure-sensitive adhesive to be used with optical members, such as thecharacteristic of inhibiting light leakage and the durability andreliability, remain excellent.

The kind of crosslinking agent that may be used in the present inventionis not particularly limited. For example, ordinary crosslinking agentssuch as an isocyanate compound, an epoxy compound, an aziridinecompound, and a metal chelate compound may be used. It is somewhatpreferable to use, but is not limited to, an isocyanate compound. Inother words, in the present invention, it is possible to select and usean ordinary crosslinking agent known in the art without limitationaccording to the kind of crosslinkable functional group included in theacryl resin, and so on. Detailed examples of the isocyanate compoundinclude, but are not limited to, at least one selected from the groupconsisting of toluene diisocyanate, xylene diisocyanate, diphenylmethanediisocyanate, hexamethylene diisocyanate, isophorone diisocyanate,tetramethylxylene diisocyanate, naphthalene diisocyanate, and a reactionproduct of one of at least one of these isocyanates and polyol (e.g.trimethylol propane). Detailed examples of the epoxy compound include,but are not limited to, at least one selected from the group consistingof ethyleneglycol diglycidylether, triglycidylether, trimethylolpropanetriglycidylether, N,N,N′,N′-tetraglycidyl ethylenediamine, and glycerindiglycidylether. Detailed examples of the aziridine compound include,but are not limited to, at least one selected from the group consistingof N,N′-toluene-2,4-bis(1-aziridinecarboxide),N,N′-diphenylmethane-4,4′-bis(1-aziridinecarboxide), triethylenemelamine, bisisoprothaloyl-1-(2-methylaziridine), andtri-1-aziridinylphosphinoxide. Further, detailed examples of the metalchelate compound include, but are not limited to, a compound in which apolyvalent metal, such as aluminum, iron, zinc, tin, titanium, antimony,magnesium, and/or vanadium, is coordinated to acetyl acetone or ethylacetoacetate.

In the pressure-sensitive adhesive composition, the crosslinking agentmay be included in an amount of 0.01 to 10 parts by weight, andpreferably 0.01 to 5 parts by weight, relative to 100 parts by weight ofacryl resin. When the content of the crosslinking agent is less than0.01 parts by weight, the cohesion of the pressure-sensitive adhesivemay be reduced. When the content of the crosslinking agent is more than10 parts by weight, interlayer peeling or lifting may occur, and thusthe durability and reliability may be reduced.

The pressure-sensitive adhesive composition of the present invention mayfurther include a silane coupling agent in addition to theabove-mentioned components. This coupling agent serves to enhancecohesiveness and adhesive stability between the pressure-sensitiveadhesive and a glass substrate, and thus improve heat resistance andmoisture resistance. Further, the coupling agent serves to increaseadhesive reliability when the pressure-sensitive adhesive is left alonefor a long time under high-temperature and/or high-humidity conditions.Examples of the coupling agent that may be used in the present inventioninclude γ-glycidoxypropyl triethoxy silane, γ-glycidoxypropyl trimethoxysilane, γ-glycidoxypropyl methyldiethoxy silane, γ-glycidoxypropyltriethoxy silane, 3-mercaptopropyl trimethoxy silane, vinyltrimethoxysilane, vinyltriethoxy silane, γ-methacryloxypropyl trimethoxy silane,γ-methacryloxypropyl triethoxy silane, γ-aminopropyl trimethoxy silane,γ-aminopropyl triethoxy silane, 3-isocyanatopropyl triethoxy silane,γ-acetoacetatepropyl trimethoxy silane, γ-acetoacetatepropyl triethoxysilane, β-cyanoacetyl trimethoxy silane, β-cyanoacetyl triethoxy silane,or acetoxyaceto trimethoxy silane, among which one or a mixture of atleast two may be used. The present invention preferably uses, but is notlimited to, a silane coupling agent having an acetoacetate group or aβ-cyanoacetyl group. In the composition of the present invention, thesilane coupling agent may be included in an amount of 0.01 to 5 parts byweight, and preferably 0.01 to 1 parts by weight, relative to 100 partsby weight of acryl resin. When the content of the coupling agent is lessthan 0.01 parts by weight, an effect of increasing the adhesion may beinsignificant. When the content of the coupling agent is more than 5parts by weight, the durability and reliability may be reduced.

Further, from the standpoint of the adjustment of adhesive performance,the pressure-sensitive adhesive composition of the present invention mayfurther include 1 to 100 parts by weight of a tackifier relative to 100parts by weight of acryl resin. The kind of tackifier is notparticularly limited. For example, the tackifier may employ one or amixture of at least two selected from a (hydrogenated) hydrocarbonresin, a (hydrogenated) rosin resin, a (hydrogenated) rosin ester resin,a (hydrogenated) terpene resin, a (hydrogenated) terpene phenol resin, apolymerized rosin resin, and a polymerized rosin ester resin. When thecontent of the tackifier is less than 1 part by weight, the effect ofadding the tackifier may be insignificant. When the content of thetackifier is more than 100 parts by weight, the effect of increasingcommercial utility and/or cohesion may be reduced.

Further, the pressure-sensitive adhesive composition of the presentinvention may further include at least one additive selected from thegroup consisting of an epoxy resin, a crosslinking agent, a UVstabilizer, an antioxidant, a coloring agent, a reinforcing agent, afiller, an anti-foaming agent, a surfactant, and a plasticizer, to theextent that it does not influence the effects of the present invention.

In the present invention, a method of preparing the pressure-sensitiveadhesive using the pressure-sensitive adhesive composition including thecomponents as mentioned above is not particularly limited.

That is, in the present invention, any method may be used as long as thepattern of hard and soft areas can be formed by altering the UV raysirradiated when the pressure-sensitive adhesive is prepared.

For example, the method of preparing the pressure-sensitive adhesive ofthe present invention may include a first step of coating a coatingsolution (e.g. a pressure-sensitive adhesive composition) for formingthe pressure-sensitive adhesive on a substrate, and a second step ofcuring the pressure-sensitive adhesive composition coated on thesubstrate in the first step so as to form a pattern of hard and softareas, whereby the soft area has a lower storage modulus than the hardarea.

In the present invention, a method of preparing the coating solutionused in the first step is not particularly limited. For example, thecoating solution may be prepared by appropriately mixing theabove-mentioned components, or by diluting the above-mentionedcomponents with an appropriate solvent in consideration of coatability.

Further, in the first step of the present invention, the kind ofsubstrate on which the coating solution is coated is not particularlylimited. For example, when the pressure-sensitive adhesive of thepresent invention is to be formed on a polarizer, the coating solutionmay be directly coated on the polarizer (e.g. a polarizing film, apolarizing element or a protecting film), or to a releasable substrateaccording to the circumstances. In the present invention, when thecoating solution is coated on a releasable substrate, a patternedadhesive may be formed through a curing process described below, andthen a process of transferring the pressure-sensitive adhesive formed inthis way to the polarizer may be additionally carried out.

Meanwhile, in the first step of the present invention, the method ofcoating the coating solution on the substrate as mentioned above is notparticularly limited, and may be carried out using a typical means suchas a bar coater.

Further, during the coating process of the first step, from theviewpoint of carrying out uniform coating, it is preferable to controlthe functional group of the multi-functional crosslinking agent includedin the pressure-sensitive adhesive composition or the coating solutionso as not to give rise to a crosslinking reaction. Thereby, themulti-functional crosslinking agent may form a crosslinking structurewhile being cured and aged after the coating, and thus improve thecohesion of the pressure-sensitive adhesive, as well as adhesivephysical properties and cuttability.

Further, before the coating solution coated in the first step of thepresent invention is applied to the curing process described below, itis preferable to sufficiently remove foam-producing components such asvolatile components or reaction residues included in thepressure-sensitive adhesive composition or the coating solution. Thisprocess can prevent the storage modulus from being lowered because ofexcessively low crosslinking density or molecular weight of thepressure-sensitive adhesive after curing, and prevent a scatter frombeing formed inside because of an increase in the size of foams existingbetween the glass substrate and the pressure-sensitive adhesive layerunder high temperature.

The second step of the present invention is a process of curing thecoating solution coated on the substrate in the first step so as to formthe pattern of hard and soft areas. In the present invention, the methodof forming the pattern of hard and soft areas is not particularlylimited. For example, the pattern of hard and soft areas may be formedby controlling the degree of curing of the coating solution inconsideration of the pattern to be formed. In detail, when a differencein the degree of curing of the coating solution is caused during thecuring process, an area in which the curing is carried out more thananother area has a higher storage modulus, which forms the hard area,whereas an area where the curing is carried out less than another areahas a lower storage modulus, which forms the soft area.

Further, the method of controlling the degree of curing of the coatingsolution (i.e. the pressure-sensitive adhesive composition) in thepresent invention is not particularly limited. For example, when aphotocurable adhesive composition is used, the degree of curing can becontrolled by controlling an irradiating dose and/or time of theradiation at each place of the coating solution according to the desiredpattern of hard and soft areas. In detail, when the irradiating dose ortime of the radiation is increased, the hardness of thepressure-sensitive adhesive may be increased to form the hard area. Incontrast, when the irradiating dose or time of the UV rays is decreased,the soft area may be formed. Further, when the irradiating radiationintensity of the UV rays is zero, the hardness of the pressure-sensitiveadhesive is controlled to the minimum extent.

In the present invention, the method of controlling the degree of curingbased on the alteration of the irradiation of the UV rays is notparticularly limited.

For example, in the present invention, the alteration of the irradiationof the UV rays may be caused through a method of performing UV spotirradiation using a laser processing apparatus or a stepper (i.e. alithography apparatus), a method of using a UV cutoff mask, or a methodof using a UV shield mask.

Among them, the UV spot irradiation method is adapted to cause adifference in the degree of curing by moving the substrate (e.g.polarizer or releasable film) on which the coating solution is formedduring UV spot irradiation, or moving the spot irradiated UV raysthemselves on a plane of the coating solution. In this process, thedifference in the degree of curing may be induced by controlling thediameter of a spot irradiated with the UV rays, the path of thesubstrate or UV light source, the irradiating radiation intensity of theUV rays, or an irradiating time of the UV rays. Here, the type of UVlight source that may be used is not particularly limited. For example,the UV light source may include a high-pressure mercury lamp, alow-pressure mercury lamp, a hydrogen (heavy hydrogen) lamp, an inertgas discharge lamp (e.g. of xenon, argon, helium or neon), a nitrogenlaser, an excimer laser (e.g. of XeCl, XeF, KrF, or KrCl), a hydrogenlaser, or a halogen laser. Further, the kind of light source that may beused in the present invention is not limited to the above-mentionedtypes. Thus, any type may be used as long as it can accomplish theobjects of the present invention. Meanwhile, the conditions of the UVrays required in the spot irradiation are not particularly limited. Forexample, UV rays having a wavelength of 400 nm to 10 nm may be used.Further, the UV rays used in the above-mentioned step may have anillumination intensity of 200 mW/cm² to 1,000 mW/cm². In addition, theUV rays used in the above-mentioned step may have a radiation intensityof 50 mJ/cm² to 1,500 mJ/cm². However, the characteristics of the UVrays such as illumination or radiation intensity are not particularlylimited, and thus may be appropriately controlled in consideration of,for instance, the desired storage modulus of the pattern to be formed.

In the case where the pattern of hard and soft areas is to be realizedusing a UV cutoff mask, the second step may include irradiating UV rayson the coating solution coated on the substrate through the UV cutoffmask.

FIG. 2 is a schematic view illustrating a pattern forming methodaccording to an embodiment of the present invention, and particularly aprocess of stacking a transparent releasable film c on a coatingsolution b formed on a substrate a (e.g. a polarizer or a releasablefilm) and then irradiating UV rays through a UV cutoff mask d.

Here, the “UV cutoff mask” may be made of a material which is capable ofcutting off the UV rays, i.e. which is capable of preventingtransmission of the UV rays. In the present invention, the material ofthe UV cutoff mask is not particularly limited. For example, an ordinarymaterial known in the art may be properly employed. In the presentinvention, a pattern through which the UV rays can be transmitted may beformed on the UV cutoff mask in consideration of a desired hard areapattern, and then the UV rays are irradiated through the UV cutoff mask.In this process, the UV rays are irradiated on the coating solution bformed on the substrate a along the pattern formed on the UV cutoff maskd, and thus the hardness of the coating solution of the area irradiatedwith the UV rays may be increased.

In the present invention, the characteristics of the irradiated UV raysare not particularly limited. For example, UV rays having a wavelengthof 400 nm to 10 nm may be used. Further, the UV rays used in this stepmay have an illumination intensity of 200 mW/cm² to 1,000 mW/cm², and aradiation intensity of 100 mJ/cm² to 1,500 mJ/cm². However, thecharacteristics of the UV rays such as illumination or radiationintensity are not particularly limited, and thus may be appropriatelycontrolled in consideration of, for instance, the storage modulus of thedesired pattern to be formed.

In the present invention, when the pattern is formed using the UV cutoffmask, subsequent to the above-mentioned step (hereinafter, referred toas “step (1)”), a step (hereinafter, referred to as “step (2)”) ofremoving the UV cutoff mask, and then irradiating the UV rays on thecoating solution again may be additionally performed.

In the present invention, from the standpoint of pattern formationefficiency, it is preferable to control the UV rays irradiated in step(2) to have a weaker intensity than the UV rays irradiated in step (1).In detail, the hardness of the pattern of the hard area formed byirradiating the UV rays in step (1) is not greatly influenced by the UVrays irradiated in step (2). As such, even if the UV rays are irradiatedin step (2) after the UV cutoff mask is removed, the pattern of the hardarea formed in step (1) can be maintained, and another area (i.e. a softarea) where the UV rays are not irradiated in step (1) is cured by weakirradiation of UV rays, so that a pattern is formed according to thedegree of curing.

Thus, in the method of the present invention, UV rays having awavelength of 400 nm to 10 nm may be used in step (2), and theillumination thereof may be controlled within a range of 200 mW/cm² to1,000 mW/cm². The radiation intensity of the UV rays may be controlledwithin a range of 400 mJ/cm² or less. However, the characteristics ofthe UV rays such as illumination or radiation intensity are notparticularly limited, and thus may be appropriately controlled inconsideration of, for instance, the desired storage modulus of thepattern to be formed.

However, the conditions of the irradiated UV rays are merelyillustrative of the present invention. In other words, in the presentinvention, the conditions of the irradiated UV rays may be freely variedin consideration of the pattern to be formed, and the pattern may beformed through only step (1) without performing step (2) in theabove-mentioned method according to circumstances.

Further, in the present invention, when the pattern of hard and softareas are to be realized using the UV shield mask, the second step mayinclude irradiating the UV rays on the coating solution coated on thesubstrate through the UV shield mask.

FIG. 3 is a schematic view illustrating a pattern forming methodaccording to another embodiment of the present invention, andparticularly a process of forming a transparent releasable film c on acoating solution b formed on a substrate a (e.g. a polarizer or areleasable film) and then irradiating UV rays through a UV shield maske.

The term “UV shield mask” as used in the present invention refers to amask made of a material having a shielding rate with respect to UV raysof about 40 to 95%, and preferably about 50 to 90%. In the presentinvention, the material of the UV shield mask is not particularlylimited. For example, an ordinary material known in the art may beproperly employed. As illustrated in FIG. 3, when a predeterminedpattern is formed on the UV shield mask, and then UV rays are irradiatedthrough the UV shield mask, the UV rays are transmitted at fullintensity through a portion where the pattern is formed, and thus strongUV rays are irradiated. In contrast, only some of the irradiated UV raysare transmitted through a portion where the pattern is not formed, andthus weak UV rays are irradiated. Thus, an area in which the UV rays arestrongly irradiated has high hardness, whereas an area in which the UVrays are weakly irradiated has low hardness. As a result, the pattern ofhard and soft areas may be formed. Further, in this step, when the UVirradiation conditions (e.g. irradiating dose and/or time) or theshielding rate of the UV shield mask are properly controlled, thedesired pattern may be efficiently formed.

In the present invention, when the pattern is formed using the UV shieldmask, UV rays having a wavelength of 10 nm to 400 nm may be used.Further, the UV rays in this step may have illumination intensity of 200mW/cm² to 1,000 mW/cm². In addition, the UV rays in this step may have aradiation intensity of 200 mJ/cm² to 1,500 mJ/cm². However, thecharacteristics of the UV rays such as illumination or radiationintensity are not particularly limited, and may be appropriatelycontrolled in consideration of, for instance, the desired storagemodulus of the pattern to be formed.

However, the UV irradiation conditions are merely illustrative of thepresent invention. In other words, in the present invention, the UVirradiation conditions may be freely varied in consideration of thedesired pattern or the shield rate of the UV shield mask.

In the present invention, subsequent to each of the above-mentionedsteps, a process of, for instance, transferring the pressure-sensitiveadhesive formed on a releasable substrate to the polarizer may beproperly performed as needed.

Further, the present invention relates to a polarizer including thepressure-sensitive adhesive of the present invention, thepressure-sensitive being formed on one or both surfaces of a polarizingfilm or element.

In the present invention, the type of polarizing film or element makingup the polarizer is not particularly limited. For example, thepolarizing film or element may be a film prepared by incorporating apolarizing component such as iodine or dichromatic dye into apolyvinylalcohol resin film, and elongating the film. Examples of thepolyvinylalcohol resin that may be used herein include, but are notlimited to, polyvinyalcohol, polyvinyl formal, polyvinylacetal, orhydrolysate of an ethylene vinyl acetate copolymer. In the presentinvention, the thickness of the polarizing film or element is notparticularly limited, and thus it is formed at a typical thickness.

Further, the polarizer may have a multilayer structure in which aprotecting film is formed on one surface or both surfaces of thepolarizing film or element. Examples of the protecting film include, butare not limited to, a cellulose film such as triacetyl cellulose (TAC),a polycarbonate film, a polyester film such as a polyethyleneterephthalate film, a polyethersulfone film and/or a polyolefin filmsuch as polyethylene film, a polypropylene film, or a polyolefin filmhaving a cyclo or norbornene structure. In the present invention, thethickness of the protecting film is not particularly limited, and thusit may be formed at a typical thickness.

The polarizer of the present invention may further include at least onefunctional layer selected from the group consisting of a protectivelayer, a reflective layer, an anti-glare layer, a phase differentialplate, a wide viewing-angle compensating film, and a brightnessimproving film, in addition to the protecting film formed on thepolarizing film or element.

In the present invention, when the pressure-sensitive adhesive is formedon the polarizer as mentioned above, it is preferable to set thedirection where the hard and soft areas of the pressure-sensitiveadhesive are formed in consideration of the direction that thepolarizing film or element is elongated. This is because the polarizingfilm or element included in the polarizer is elongated in one directionin the process of preparation in order to produce a polarizationproperty, and thus the polarizer suffers from reduction in dimensionalstability, particularly in the direction of elongation.

Thus, for example, as illustrated in FIG. 4 or 5, the hard areas 4-1 or5-1 is formed on the pressure-sensitive adhesive 4 or 5 in the shape ofa continuous line, and the linear hard area 4-1 or 5-1 is formedparallel to the direction of elongation A of the polarizing film orelement. The linear hard areas 4-1 or 5-1 formed on thepressure-sensitive adhesive 4 or 5 may effectively inhibit a dimensionalchange caused by shrinkage or expansion of the polarizer.

In detail, the polarizer of the present invention may include thepolarizing film or element, and the pressure-sensitive adhesive formedon one or both surfaces of the polarizing film or element, and the hardarea of the pressure-sensitive adhesive may be patterned in the shape ofa line, preferably a continuous line, and the linear hard area may beformed parallel to the direction of elongation of the polarizing film orelement.

Further, in the present invention, as illustrated in FIG. 6 or 7, thehard areas 6-1′ or 7-1′ of the pressure-sensitive adhesive 6 or 7included in the polarizer may be patterned in the shape of a lineperpendicular to the direction of elongation A of the polarizing film orelement. If necessary, in order to maximize an effect obtained byforming the pattern of the hard area, as illustrated in FIG. 8 or 9, thepressure-sensitive adhesive 8 or 9 of the present invention may includeboth the linear hard areas 8-1 or 9-1 formed in a direction parallel tothe direction of elongation A of the polarizing film or element and thelinear hard areas 8-1′ or 9-1′ formed in a direction perpendicular tothe direction of elongation A of the polarizing film or element.

In detail, the polarizer of the present invention may include thepolarizing film or element, and the pressure-sensitive adhesive formedon one or both surfaces of the polarizing film or element, and the hardarea of the pressure-sensitive adhesive may be patterned in the shape ofa line, preferably a continuous line, and the linear hard area may beformed perpendicular to the direction of elongation of the polarizingfilm or element.

The present invention also relates to a liquid crystal display (LCD)including a liquid crystal panel in which the polarizer of the presentinvention is attached to one or both surfaces of a liquid crystal cell.

The type of liquid crystal panel included in the LCD of the presentinvention is not particularly limited. For example, the liquid crystalpanel may employ all types of known liquid crystal panels, which includea passive matrix type such as a twisted nematic (TN) type, a supertwisted nematic (STN) type, a ferroelectric (F) type, or a polymerdispersed (PD) LCD type, an active matrix type such as a two terminaltype and a three terminal type, an in-plane switching (IPS) type, and avertical alignment (VA) type. Further, the other components included inthe LCD and their manufacturing methods are not particularly limited,and thus may be used by adopting a typical configuration of the relatedart with no limitation.

EXAMPLES

Hereinafter, the present invention will be described in greater detailwith reference to the following examples and comparative examples, butthe scope thereof is not restricted to these examples.

Preparation Example 1 Preparation of Acryl Resin A

100 parts by weight of n-butyl acrylate (n-BA) was added to a 1 Lreactor in which nitrogen gas was refluxed, and which had a cooler foradjustment of temperature installed. Then, 120 parts by weight of ethylacetate (EAc) was added as a solvent, and then the reactor was purgedwith nitrogen gas for 60 minutes in order to remove oxygen. After that,the reactor was kept at a temperature of 60° C., and 0.05 parts byweight of azobisisobutyronitrile (AIBN) were added as a reactioninitiator, and reacted for 8 hours. After the reaction was completed,the reacted product was diluted with EAc (solid content: about 15 wt %).Thereby, an acryl resin A having a weight-average molecular weight of1,850,000 and a molecular weight distribution Mw/Mn of 5.5 was prepared.

Preparation Example 2 Preparation of Acryl Resin B

An acryl resin B having a weight-average molecular weight of 1,910,000and Mw/Mn of 4.9 was prepared through the same process as in Example 1,except that a monomer mixture including 99 parts by weight of n-butylacrylate (n-BA) and 1 part by weight of 2-hydroxyethyl acrylate wasused.

Preparation Example 3 Preparation of Pressure-Sensitive AdhesiveComposition (Coating Solution) C

Relative to 100 parts by weight of the acryl resin A, 15 parts by weightof tris(acryloxyethyl)isocyanurate (trifunctional type, M315) as amulti-functional acrylate, and 1.0 part by weight of hydroxyl cyclohexylphenyl ketone (Irg 184, available from Ciba Specialty Chemical Corp.,Switzerland) as a photo initiator were mixed. Thereby, apressure-sensitive adhesive composition C was prepared.

Preparation Example 4 Preparation of Pressure-Sensitive AdhesiveComposition (Coating Solution) D

Relative to 100 parts by weight of the acryl resin B, 0.5 parts byweight of TDI isocyanate crosslinking agent (Coronate L, NipponPolyurethane Co. Ltd., Japan) as a multi-functional crosslinking agent,15 parts by weight of tris(acryloxyethyl)isocyanurate (trifunctionaltype, M315) as multi-functional acrylate, and 1.0 part by weight ofhydroxyl cyclohexyl phenyl ketone (Irg 184, available from CibaSpecialty Chemical Corp., Switzerland) as a photo initiator were mixed.Thereby, a pressure-sensitive adhesive composition D was prepared.

Examples 1 through 7 and Comparative Examples 1 and 2

As shown in Table 1 below, a pressure-sensitive adhesive where hard andsoft areas were patterned was prepared using the pressure-sensitiveadhesive composition prepared in Preparation Example 3 or 4. Here, thepatterns of the hard and soft areas were formed using a UV cutoff maskor a UV shield mask. The corresponding method will be described below indetail. In the case of Comparative Example 2, uniform UV rays wereirradiated on the entire surface of a coating solution, therebyadjusting the storage modulus. No step for forming the patterns wastaken.

Use of UV Cutoff Mask (Method A)

The formation of the pattern using the UV cutoff mask was carried outaccording to the method shown in FIG. 2. In detail, thepressure-sensitive adhesive composition prepared in each PreparationExample was coated on a transparent releasable film c (PET film, MRF-38,available from Mitsubishi Polyester Film Co. Ltd.) having a thickness of38 μm (to have a thickness of 23 μm after being dried), and was thendried in an oven at 110° C. for 3 minutes. Subsequently, the driedcoating layer b was attached to a polarizer a, and then UV rays wereirradiated from the side of the releasable film c through the UV cutoffmask d having a pattern.

The UV cutoff mask d was brought into contact with the releasable film cto the utmost extent, thereby minimizing a gap between the releasablefilm c and the UV cutoff mask d. The pattern of the UV cutoff mask d wasformed in the shape of a line parallel to the direction of elongation ofthe polarizing film as illustrated in FIG. 4, or was formed in twodirections, which were parallel and perpendicular to the direction ofelongation as illustrated in FIG. 8. The width of the pattern was set toabout 100 μm.

Further, the UV rays were first irradiated through the UV cutoff mask d(primary irradiation), and then irradiated again after the UV cutoffmask d was removed (secondary irradiation). In this case, the UV rayswere irradiated with an illumination intensity of 600 mW/cm² while onlythe radiation intensity was varied as follows.

Primary Irradiation of UV Rays

UV Irradiator: high-pressure mercury lamp

Illumination intensity: 600 mW/cm²

Radiation intensity: 200 mJ/cm², 400 mJ/cm², 800 mJ/cm², and 1,200mJ/cm²

Secondary Irradiation of UV Rays

UV Irradiator: high-pressure mercury lamp

Illumination intensity: 600 mW/cm²

Radiation intensity: 100 mJ/cm², 200 mJ/cm², and 400 mJ/cm²

Use of UV Shield Mask (Method B)

The formation of the pattern using the UV cutoff mask was carried outaccording to the method shown in FIG. 3. In detail, thepressure-sensitive adhesive composition prepared in each PreparationExample was coated on a transparent releasable film c (PET film, MRF-38,available from Mitsubishi Polyester Film Co. Ltd.) having a thickness of38 μm (to have a thickness of 23 μm after being dried), and was thendried in an oven at 110° C. for 3 minutes. Subsequently, the driedcoating layer b was attached to a polarizer a, and then UV rays wereirradiated from the side of the releasable film c through the UV shieldmask e having a pattern.

The UV cutoff mask d was brought into contact with the releasable film cto the utmost extent, thereby minimizing a gap between the releasablefilm c and the UV shield mask c. The pattern of the UV shield mask c wasformed in the shape of a line parallel to the direction of elongation ofthe polarizing film as illustrated in FIG. 4, or was formed in twodirections parallel and perpendicular to the direction of elongation asillustrated in FIG. 8. The width of the pattern was set to about 100 μm.A UV shielding rate of portions where the pattern was not formed was setto about 87.5%. When the UV shield mask e was used, the UV irradiationconditions were as follows.

UV Irradiation Conditions

UV Irradiator: high-pressure mercury lamp

Illumination intensity: 600 mW/cm²

Radiation intensity: 800 mJ/cm²

TABLE 1 Comparative Example Example 1 2 3 4 5 6 7 1 2 Pressure-sensitiveC C C C C C D D C adhesive Composition UV Irradiation A A A A A B A — —method Mask Type FIG. 4 FIG. 4 FIG. 4 FIG. 4 FIG. 8 FIG. 4 FIG. 4 — — UVPrimary 800 1,200 400 800 800 800 800 — 800 radiation Secondary 200 200100 — 200 200 200 — — intensity

With respect to the pressure-sensitive adhesive or the polarizerprepared in each of the Examples and Comparative Examples, the physicalproperties thereof such as gel fraction, adhesion, removability,durability and reliability, light transmission uniformity, storagemodulus, etc. were measured.

1. Measurement of Gel Fraction

The prepared pressure-sensitive adhesive was left in a constanttemperature and humidity chamber (23° C. and 60% of relative humidity(R.H.)) for about 7 days, and then about 0.3 g of the adhesive wassampled, and put into a stainless wire netting of 200 meshes. Then, thepressure-sensitive adhesive was deposited in EAc, and was stored in aroom-temperature darkroom for 3 days (72 hours). After that, the wirenetting was taken out. Undissolved parts of the adhesive were separated,and dried in an oven at 70° C. for 4 hours, and the weight (i.e. theweight of the dried undissolved parts) thereof was measured. Then, thegel fraction thereof was measured using Equation 1 below.Gel Content=B/A×100  [Equation 1]

where A represents the weight (0.3 g) of the pressure-sensitive adhesivebefore it was deposited in EAc, and B represents the weight of the driedundissolved parts after being deposited in EAc.

2. Evaluation of Adhesion and Removability

The prepared polarizer was cut to a size of 25 mm (width)×100 mm(length), and thereby a sample was prepared. A releasable film wasremoved from the sample, and the sample was attached to alkali-freeglass via the pressure-sensitive adhesive using a laminator.Subsequently, the sample was compressed in an autoclave (at 50° C. and 5atm) for about 20 minutes, and stored for 24 hours under constanttemperature and humidity conditions (23° C. and 50% R.H.). Thereby, aspecimen was prepared. After that, the adhesion strength of the specimenwas measured under conditions of a peeling speed of 300 mm/min and apeeling angle of 180° using a texture analyzer (Stable Micro SystemLtd., England). Thereby, the removability was evaluated according to thefollowing criteria.

◯: when the adhesion strength after 1 day was 800 gf/25 mm or less.

Δ: when the adhesion strength after 1 day was 1,000 gf/25 mm or more.

x: when the adhesion strength after 1 day was 2,000 gf/25 mm or more.

3. Evaluation of Durability and Reliability

The prepared polarizer was cut to a size of 180 mm (width)×250 mm(length), and thereby a sample was prepared. A releasable film wasremoved from the sample, and the sample was attached to a 19-inchcommercial panel using a laminator. Subsequently, the sample wascompressed in an autoclave (at 50° C. and 5 atm) for about 20 minutes,and stored for 24 hours under constant temperature and humidityconditions (23° C. and 50% R.H.). Thereby, a specimen was prepared.After that, in order to evaluate humidity and heat-resistant durabilityof the prepared specimen, the specimen was left under conditions of 60°C. and 90% R.H. for 500 hours, and then it was evaluated as to whetheror not bubbles appeared or peeling occurred (humidity and heat-resistantconditions). Further, to evaluate heat-resistant durability, thespecimens were left at 90° C. and 105° C. for 500 hours, and then it wasevaluated as to whether or not the bubbles appeared or peeling occurred(heat-resistant conditions). All the specimens were evaluated afterbeing left at room temperature for 24 hours just before their stateswere evaluated. The criteria for evaluating the humidity andheat-resistant characteristics and the heat-resistant characteristicswere as follows.

◯: when neither the bubbles nor the peeling occurred.

Δ: when the bubbles and/or the peeling occurred slightly.

x: when the bubbles and/or the peeling occurred considerably.

4. Light Transmission Uniformity

The light transmission uniformity was evaluated by observing whether ornot there was a portion where light leaks out through a polarizer in adarkroom using a backlight. In detail, a polarizer having thepressure-sensitive adhesive layer was attached to a 22-inch monitor(available from LG Philips LCD Co. Ltd.), and it was stored underconstant temperature and humidity conditions for 1 day and left in anoven at 80° C. for 200 hours. Then, the light transmission uniformity ofcircumferences of four edges of the monitor was evaluated using thebacklight. The criteria for evaluating the light transmission uniformitywere as follows.

{circle around (●)}: when the light transmission uniformity in thecircumferences of the four edges of the monitor was hardly observed withthe naked eye.

◯: when the light transmission uniformity in the circumferences of thefour edges of the monitor was slightly observed with the naked eye.

Δ: when the light transmission uniformity in the circumferences of thefour edges of the monitor was somewhat observed with the naked eye.

x: when the light transmission uniformity in the circumferences of thefour edges of the monitor was considerably observed with the naked eye.

6. Measurement of Storage Modulus of Adhesive

The pressure-sensitive adhesive coated between releasable films was cutto a size of 15 cm×25 cm, and one of the releasable films was removed.Then, the pressure-sensitive adhesive was laminated five times until thethickness thereof was about 1 mm. Subsequently, the laminate was cut inthe shape of a circle having a diameter of 8 mm, compressed by glass,and left overnight to increase wettability on an interface between therespective layers as well as remove bubbles generated during lamination.Thereby, a specimen was prepared. Next, the specimen was placed on aparallel plate, and a gap was adjusted. Then, the storage modulus wasmeasured after zero points of normal and torque were adjusted, andstabilization of a normal force was checked.

Measurement Apparatus and Conditions

Measurement apparatus: ARES-RDA having a forced convection oven,available from TA Instruments Inc.

Measurement Conditions:

1) geometry: 8 mm parallel plate

2) gap: about 1 mm

3) test type: dynamic strain frequency sweep

4) strain: 10.0%,

5) temperature: 30° C.

6) initial frequency: 0.4 rad/s, and

7) final frequency: 100 rad/s.

The results of the measurement as mentioned above are arranged in Table2.

TABLE 2 Comparative Example Example 1 2 3 4 5 6 7 1 2 G′_(hard) (MPa)10.1 42.5 6.6 10.1 10.1 10.1 10.1 0.30 10.1 G′_(soft) (MPa) 1.3 1.3 0.80.11 1.3 1.3 1.3 0.30 10.1 RG′ 7.8 32.7 8.3 91.8 7.8 7.8 7.8 1 1 HP area(%) 30 20 40 50 40 30 30 0 0 Gel Content (%) 93 94 94 61 95 92 92 81 95Adhesion (gf/25 mm) 340 250 270 390 305 330 220 750 120 Removability ∘ ∘∘ ∘ ∘ ∘ ∘ ∘ ∘ Heat-  90° C. ∘ ∘ ∘ ∘ ∘ ∘ ∘ Δ Δ resistant 105° C. ∘ ∘ ∘ ∘∘ ∘ ∘ x x Durability Humidity and Heat- ∘ ∘ ∘ ∘ ∘ ∘ ∘ x x resistantDurability Light Transmission ⊙ ⊙ ⊙ ⊙ ⊙ ⊙ ⊙ x ∘ Uniformity G′_(hard):storage modulus of hard area G′_(soft): storage modulus of soft areaRG′: ratio of storage moduli of hard and soft areas(G′_(hard)/G′_(soft)) HP area: proportion of hard area with respect toentire area of adhesive

As can be seen from the results of Table 2, Examples 1 through 7 of thepresent invention in which the pattern of hard and soft areas was formedin the single pressure-sensitive adhesive show excellent durability andreliability under high-temperature or high-humidity conditions, andmaintain excellent physical properties such as adhesion andremovability. Further, when applied to a monitor having a large size of22 inches, Examples 1 through 7 of the present invention showedexcellent light transmission uniformity.

In contrast, in the case of Comparative Example 1 in which the storagemodulus of the entire surface of the pressure-sensitive adhesive wasrelatively low, the shrinkage and expansion caused by the strain of thepolarizer was not effectively inhibited, so that the light leakage waswidely distributed, and the durability and reliability was very weak.Further, in the case of Comparative Example 2 in which the storagemodulus of the entire surface of the pressure-sensitive adhesive wasrelatively high, the hardness of the pressure-sensitive adhesive wasincreased, so that the pressure-sensitive adhesive did not producesufficient adhesion strength, and the durability thereof was greatlyreduced.

It can be confirmed from the above-mentioned results that, in the statewhere the storage modulus of the entire surface of thepressure-sensitive adhesive is equally controlled, thepressure-sensitive adhesive cannot easily produce an excellent effecteven through adjustment of the storage modulus.

The pressure-sensitive adhesive of the present invention has excellentdurability and reliability under high-temperature or high-humidityconditions as well as excellent physical properties such as tackiness,removability and workability. Further, the pressure-sensitive adhesiveof the present invention represents high stability with respect tostrain caused by the shrinkage and expansion of the polarizing elementwhen applied to, for instance, a polarizer, so that light leakage can beeffectively prevented when the pressure-sensitive adhesive is applied toa large-sized display. Thus, the present invention provides apressure-sensitive adhesive having excellent durability and reliability,tackiness, workability, removability, and of the ability to inhibitlight leakage under high-temperature or high-humidity conditions, amethod of producing the pressure-sensitive adhesive, a polarizer havingthe pressure-sensitive adhesive, and a liquid crystal display having thepolarizer.

While the invention has been shown and described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in font and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

What is claimed is:
 1. A method for preparing a pressure-sensitiveadhesive, comprising: a 1^(st) step of coating a coating solution forforming the pressure-sensitive adhesive on a substrate; and a 2^(nd)step of forming a pattern of a hard area and a soft area, whereby thesoft area has a lower storage modulus than the hard area, by curing thecoating solution coated on the substrate.
 2. The method according toclaim 1, wherein the 2^(nd) step includes performing spot irradiation ofultraviolet rays to form the pattern.
 3. The method according to claim2, wherein the ultraviolet rays have an illumination intensity of 200mW/cm² to 1,000 mW/cm².
 4. The method according to claim 2, wherein theultraviolet rays have a radiation intensity of 50 mJ/cm² to 1,500mJ/cm².
 5. The method according to claim 1, wherein the 2^(nd) stepincludes irradiating ultraviolet rays on the coating solution coated onthe substrate through an ultraviolet cutoff mask.
 6. The methodaccording to claim 5, wherein the ultraviolet rays have an illuminationintensity of 200 mW/cm² to 1,000 mW/cm².
 7. The method according toclaim 5, wherein the ultraviolet rays have a radiation intensity of 100mJ/cm² to 1,500 mJ/cm².
 8. The method according to claim 5, furthercomprising irradiating the ultraviolet rays on the coating solutionafter removing the ultraviolet cutoff mask.
 9. The method according toclaim 8, wherein the ultraviolet rays have an illumination intensity of200 mW/cm² to 1,000 mW/cm².
 10. The method according to claim 8, whereinthe ultraviolet rays have a radiation intensity of 400 mJ/cm² or less.11. The method according to claim 1, wherein the 2^(nd) step includesirradiating ultraviolet rays on the coating solution coated on thesubstrate through an ultraviolet shield mask.
 12. The method accordingto claim 11, wherein the ultraviolet shield mask has a shield rate of40% to 95% with respect to the ultraviolet rays.
 13. The methodaccording to claim 11, wherein the ultraviolet rays have an illuminationintensity of 200 mW/cm² to 1,000 mW/cm².
 14. The method according toclaim 11, wherein the ultraviolet rays have a radiation intensity of 200mJ/cm² to 1,500 mJ/cm².